The invention relates to an optical cable element having a core and at least one optical fiber which is provided around the core. The cable element may also comprise a separate secondary coating of a synthetic resin.
Such an optical cable element is known, inter alia, from an article by F. Krahn et al. entitled "The manufacture of optical cables" and from an article by O. R. Bresser entitled "Metal-free optical fibre cables" (Philips Telecommunications Review, Volume 37, No. 4, September 1979, pp. 231-240 and pp. 251-256, respectively. The optical cable element known from these references comprises a central core manufactured from an aromatic polyamide synthetic resin of high density. The resin may be, for example, the polyamide synthetic resin known by the tradename of Kevlar.
Six optical fiber are twisted around the core in spiral form on the surface of the core. Each optical fiber has a separate secondary coating provided by an extrusion process. The secondary coating is manufactured from polyvinylidene-difluoride. Within the secondary coating the fiber can move freely.
Polyethylene foil is wound around the cable element. The foil is covered with an extruded synthetic resin sheath of, for example, polyethylene which may be reinforced with glass fiber.
It is stated on page 255 of the article by Bresser that the pulling forces exerted on the cable element, for example upon installation thereof, act on the outside of the element and have to be taken up and compensated for by the core. The secondary coating may not be used to transmit the pulling forces to the central core, so the cable element must be provided with an external strain relieving element.